Dropping In An X302 Crate Engine Gets An Old Fox Up To Speed

Tom Wilson

November 1, 2010

This is a crate engine story that talks about everything except the crate engine. We did that last month when we detailed our new M-6007-X302 engine.

Just in case you missed it, the X302 is Ford Racing's affordable stock-block small-block. At a competitive $3,495, it's ideal for real-world projects, either fuel-injected, such as our '91 5.0 LX hatchback, or carbureted. Under best conditions, it's rated at 340 hp and has a rumpty-rump E303-cam persona.

This month we address everything else surrounding a crate-engine install. That's because it's natural to get excited about the crate motor and the intake or blower you're going to put on it, but oh-too-easy to overlook the mundane, such as engine mounts, fan clutches, and radiator hoses. It sounds pedantic, but you must have a plan. An engine change is relatively easy work-a collection of many small, easy steps-but the key word is "many." Not thinking it through is begging for frustration and disappointment.

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The first step is setting the scope of the work. Are you changing just a blown engine in an otherwise great-running car? Or, like us, are you making the pivotal improvement on a high-mileage daily driver? Obviously, you need to set a budget.

As you think through where you want to be at the end of the project, we think you'll be surprised at how many parts you want to change besides the core engine. Don't be surprised when your simple crate-engine job turns into a full-car restoration. That's what happened to us.

Our case is hyper-typical. Our '91 LX hatchback had 198,062 miles when it's original engine came out. As a daily driver, the car was up and running, but it was used up in so many mechanical ways. The valve covers and oil pan had never been off, nor had we changed the ignition wires or upgraded the stock exhaust manifolds. The radiator had who knows how much gunk in its tubes, the power steering pump was grrrring a little, the engine mounts had sagged. Furthermore, the clutch was unknown, the transmission noisy, and the U-joints were likely original.

We opted to change everything. Along with recent upholstery and other interior work, plus cutting and polishing the paint, a new set of mechanicals would give us a fairly new Fox-and no new car payments, big insurance, or registration bills.

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Parts Gathering
We're covering most of our parts details in the photos and captions, but in general overview, consider the following. You need a place to work. Do you have a home shop? Great. If not, go with a local shop. We chose GTR Performance, and the staff not only did the work, but provided indispensible knowledge and support services (receiving, research, and bargaining with suppliers).

All crate engines come bare from at least the valve covers on up. Select the intake manifold, throttle body, and cold-air intake that work with your heads and cam. We chose Edelbrock's Performer RPM II because it's a good power maker and has an E.O. number.

What about your front-of-engine accessories? The alternator, water pump, power steering, and so on are normally changed as-needed, but you might want to upgrade now to reset the clock on high-mileage units and gain shiny new parts to match your new engine.

Interestingly, we swapped what we thought was a noisy but still working power steering pump against Ricardo Topete's recommendation at GTR. He was right. Our zillion-mile PS pump was much quieter than the one we got from NAPA. Water pumps we would change no questions asked, but alternators, air pumps, and so on we'd clean and re-use.

If the original radiator is old or you're stepping up the power with the new crate engine, then a new radiator is smart; ditto for the fuel system. Old in-tank fuel pumps, tired filters, and new injectors don't mix.

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Which brings up injectors-are they properly sized for the crate motor you're installing? You need new engine mounts unless you already have aftermarket mounts. We recommend urethane mounts as they hardly affect vibration but are vastly more durable than rubber. Don't forget to change the transmission mount, too.

Moving beyond the engine compartment, consider the clutch, transmission, and driveshaft, dealing with each as necessary. Unless you just installed a new clutch, plan on a new one with the new engine. Transmissions are typically OK and most Mustang transmissions are easy enough to change on their own, so they need not be changed automatically along with the engine.

Driveshafts are forever, but U-joints aren't. Replace them as necessary is the fiscally responsible advice; we swapped in an FRPP aluminum driveshaft to easily gain new U-joints and lose a few pounds.

And what about the rest of the car? Are the tires good? Do you need a brake upgrade to match your new power? The cost must be factored into the budget and the parts acquired before grabbing the wrenches.

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Making the Swap
We don't have the room here to detail an engine change step-by-step, but in general, it's best to unhook the original engine enough to lift it out of the car, then strip it as necessary while it's out on the ground. At the same time, the new crate engine can be dressed with as much as you can get away with-headers are a joy to install out of the car-then put into the car.

Remove the vulnerable radiator before the engine, and you'll find pulling the transmission makes handling the engine that much easier. You might want to support the rear of the engine with a floor jack or stand once the transmission is out, especially if the engine mounts are shot.

Obviously you need some large tools, such as an engine hoist. A transmission jack and muffler stand (if you're lucky enough to work on a hoist) are nice, but not absolutely necessary. A suitable concrete floor is a must, and it's best to plan on having the car down for a week, typically because last-minute parts are required. A helper or two are mandatory in spots as well. For these reasons, most folks opt for pro installation, but if you have the tools, go for it.

Air conditioning turned out to be the least of our installation worries. By unbolting the compressor from the engine and laying it over a fender, it was possible to swap engines without breaking into the air conditioning system. That means no trip to an AC shop to have the system discharged and refilled later. You have to work around the bulky AC hoses and compressor, but it's still the best option.

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Because we wanted functioning EGR, we wanted to use the stock threaded fittings at rear of each head. These came blocked with steel fittings on the X302, and sealed with red Loctite. They wouldn't unscrew, so Ricardo drilled them to form an air passage. Greasing the drill bit and fishing for leftover chips with a magnet got the job done. As there is no gasket at this head-to-EGR-pipe connection, Ricardo used copper ultra-high-temp RTV silicone as a gasket.

If you have stock rubber heater hoses sticking out of the firewall, carefully remove them. Slitting them lengthwise first is smart as the heater-core nipples have a tendency to rot and pull out now that Fox heater cores are 20 years old. This begs the smart decision to replace the heater core-a hateful under-dash job you just might have to put off for a few more paychecks. If so, and your Fox already has silicone hoses, just leave 'em. The hoses might be slightly stained, but they can be safely reused, thus avoiding a wrestling match with a weakened heater core.

Finally, consider what to do with your old engine. Most people are happy enough to donate the old hulk to the install shop. Also, a used T-5 transmission that isn't beat to death is trade-worthy, so you might inquire if your core parts have any value to the shop.

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And value is just what the fresh engine will bring to your used 'Stang. If you do the job right, this kind of upgrade should bring years more enjoyment to your classic Mustang.

On The Dyno
The last two miles our 198,062-mile stock engine made were on GTR's chassis dyno. It put out an excellent 207 hp to the tire. Helping factors were underdrive pulleys and precious little internal engine friction. It was, you might say, well broken in.

Don't let the power fool you, however. The old engine burned oil like a steamship smokestack-when it wasn't pouring out of the front crank seal and oil level sender-plus the oil pressure was dangerously low and wavering with rpm. It was surely ready to spin a bearing. Moreover, it was with one part per million from passing its next smog test.

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Our new X302 bumped the needle to 270 hp tuned with 13 degrees of initial timing and the fuel ratio leaned to 12.6:1. That seems under-achieving compared to the advertised 340 hp, but not really. Ford rates these engines with a carburetor, short-runner intake manifold, and long-tube headers. At the tire, 340 flywheel horsepower would be 289 rwhp, and you still need to subtract a bunch for the long-tube headers and short-runner intake.

Looking at it the other way, Ricardo says he typically sees 280 rwhp for a street-legal "head, intake, and cam" 5.0 such as ours. Swapping back to our underdrive pulleys would put an additional 10 hp on the clock, plus a couple more for a K&N air filter and cold air intake, and maybe a touch less fuel for 282 rwhp. (We have a paper filter and stock rubber inlet hose.) Either way, that puts our X302 right where it belongs, and it will only get better with more break-in miles.

Speaking of break-in-our X302 had just 603 miles on it when dyno'd. We're sticking with mineral oil until 3,000 miles. That's Ricardo's normal recommendation before switching to synthetic.

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Even at these most conservative numbers, our X302 gained 63 hp over our original stocker-you could say it really gained 73 hp if you account for the underdrive pulleys. Even better, we were expecting to decisively lose bottom-end torque, but really didn't lose that much. The numbers wander back and forth between the two engines below 3,300 rpm, and you can squeak the numbers by playing with ignition timing, so we're calling it nearly a draw to that point as the area under the torque curve about evens out.

Above 3,300 rpm the X302 simply soars away from the old 5.0 in both power and torque. All said, great results for a crate engine that's less expensive than rebuilding the old engine!

Transmission Upgrade
Because our '91's T-5 gearbox had 198,000 miles on it and was making increasingly more gear whine, we installed Ford Racing's M-7003-Z transmission as a replacement. This is the world-class version of the venerable T-5, a transmission we've come to love for its light shifting and minimal weight.

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Compared to our tired stocker, the M-7003-Z features upgraded synchronizers and bearings; a steel input bearing retainer; more torque capacity at 330 lb-ft; a short-throw shifter (not too short and fun to shift); double-moly second, third, and countershaft cluster gears; carbon-fiber third/fourth blocker rings; and a Cobra-style pocket bearing. The rest is compatible with the stock trans, with a 28-spline output shaft and seven-tooth speedometer drive gear, so it bolts right in.

T-5 Gear Ratios

Gear

Stock '91

FRPP

1

3.35

2.95

2

1.99

1.94

3

1.33

1.34

4

1.00

1.00

5

0.68 (0.675)

0.63

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As the chart shows, the gear ratios are slightly different. Clearly the taller first gear combined with our crate engine's lower off-idle torque, choppy idle and stock 3.08 rear axle gears means starting from a dead stop is something of a small event, requiring a touch of technique. We stalled the engine numerous times until we ingrained the slight rpm increase and clutch slip required; now it's second nature. Curiously we find the taller first gear handier in parking lots, on super bumpy roads, and so on, but maybe not as brainless in crawling stop-and-go traffic.

Another consideration is speedometer error. Of course, we can ignore the First gear speedo error, Second and Third are close enough to not count, Fourth is identical, leaving only Fifth as an issue which we're probably just going to live with. In the real world, the speedometer is "slow" by about 6 mph at 70 mph in our pacing tests, so we remind ourselves we're going faster than indicated on the freeway. Ssadly, the odometer no longer reflects the exact mileage, but it's close enough for maintenance work.

What is to like about the ratios is the slightly taller Fifth gear makes flying along with the reality of 80-mph freeway traffic easier, plus it's beneficial for fuel economy at less frenetic cruise speeds. What was unexpected on the freeway-and has nothing to do with such minimal gear changes-is the noise level of the exhaust. The only new exhaust bits are the short-tube headers; the sound quality is the same-there's just a bunch more of it.